1. Field of the Invention
The present invention relates to a boost device for nonvolatile memories with and integrated stand-by charge pump.
2. Description of the Related Art
As is known, when a memory device is not used, most of its internal circuits are switched off so as to reduce consumption (waiting or stand-by phase). However it is necessary to keep some circuits operating to allow a faster return of the memory device from stand-by to the main operating condition (user-mode). In particular, during stand-by, the stand-by charge pump, which feeds the memory cell of the device with a voltage close to the reading voltage, is kept on.
On this matter, FIG. 1 shows a stand-by charge pump 1, of the diode type with two opposed phases, included in a memory device 2.
In greater detail, the stand-by charge pump 1 comprises a plurality of stages 3 connected in series between a supply line 4, set at a supply voltage Vcc, and an output terminal 5 connected to an output capacitor 6, on which an output voltage Vout is present. Each stage 3 comprises a boost capacitor 7 and a switch 8, implemented by a diode, which is switched on or off alternately with the adjacent one. The charge transfer from one stage to the other takes place under the control of phase signals CK and CKn which are complementary to each other. The value of the output voltage Vout is given by the equation:
Vout=(N+1)*(Vccxe2x88x92Vth) 
where Vth is the threshold voltage of each diode and N is the number of stages 3 of the stand-by charge pump 1.
As previously stated, the stand-by charge pump comes into operation only when the memory device is in stand-by. Consequently, during stand-by there is a considerable consumption of energy since the stand-by charge pump needs a certain time to supply the memory device with a voltage close to the reading voltage.
Moreover, the problem of area occupation is serious because the stand-by charge pump is distinct from the main charge pump, which is used during programming and reading of the memory device, and each charge pump occupies a not negligible area, since it comprises high capacities.
An embodiment of the present invention is to overcome the limitations and drawbacks indicated above with reference to the prior art.
According to the present invention a boost device for nonvolatile memories with an integrated stand-by charge pump is provided by a boost device for nonvolatile memories, comprising a charge pump circuit having an input and a first output, the charge pump circuit comprising at least one input stage and a first output stage cascade-connected between the input and the first output of the charge pump circuit, characterized in that the charge pump circuit comprises a second output stage connectable in parallel to the first output stage.